A technology of invalid stroke elimination is disclosed in Patent Documents 1 and 2. In the technology, in order that a torque can be received on a transmission side without delay in relation to an input of an engine torque in response to an accelerator pedal operation, at the time when a starting clutch is transferred from a disengaged state into an engaged state, a stand-by oil pressure is applied to an oil passage of the starting clutch after disengagement of the starting clutch, to thereby reduce or eliminate a clearance generated in the clutch.
In Patent Document 3, there is disclosed a technology wherein a high pressure is exerted at an initial stage of invalid stroke elimination at which the throttle position starts to open from a fully closed state, and thereafter the pressure is suppressed to a low level, thereby completing the invalid stroke elimination.
Where a clutch piston is moved by thus applying the stand-by oil pressure until the invalid stroke is eliminated, it is ensured that when an oil pressure thereafter acts on the clutch piston, a forward clutch can immediately start engaging. Therefore, a quick gear shift can be performed.